After the summer festival season has waned, after all the giddiness of its Florences and its Little Boots has subsided, life begins to feel something like a new term. There comes a seasonal shift in my music cravings at this time of year, a change in the light, somehow, a drop in the temperature. "I think new years begin in September, or at least for me they always have," as George Pringle put it. "I've always been fond of September. Spring is never a good time; it's a trussed-up and beautiful drag queen. But autumn is real."

There has been some of that cool new bluster recently in the music of the xx, Mumford and Sons, AA Bondy and the particular bittersweet twinge in Richard Hawley singing Don't Get Hung Up in Your Soul. But lately the mornings have been soundtracked by Stornoway, their music seeming to strike the same note as the sharp sunlight and the faint chill underfoot. "Conkers shining on the ground, the air is cooler, and I feel like I just started uni," their debut single, Zorbing, begins.

Stornoway, as you may be aware, are a six-piece from Oxford, who describe themselves as consisting of "an ­ornithologist, a rusty Russian translator and a South African brotherhood," and they are still quite shamefully unsigned. They play double bass and trumpet and cello and violin and banjo, and succeed in knitting Irish inflection to bluegrass intonation to create a sound that is richly, greenly, surprisingly British.

There is something instinctively charming about this band: one of their songs carries the sound of them chopping carrots and sawing wood, and apparently they once bought all the crockery in a branch of Age Concern so that they could record its destruction. Another story has them happily ­winning a bowl of fruit in a university talent ­contest after finishing second to a group of Norse singers. ­Perhaps my favourite moment at this year's Glastonbury was cramming ­Stornoway and all their instruments into the Guardian camper van, and forcing them to play for us while the rain fell outside.

And there is a quality, too, to their music that particularly fits this time of year – a melodic optimism, perhaps, a wistful delight. Ostensibly a song inspired by the extreme sport invented in New Zealand, Zorbing was simultaneously a perfect embodiment of that first crisp taste of love. "I've been singing you this song inside a bubble," it ran, against the brass and swell of barbershopped voices. "Been zorbing through the streets of Cowley."

Another track, Fuel Up, bottles that strange autumnal ache for the passage of time. "Open your eyes and you're nine years older/ Hands on the wheel, and you're racing on over to lie with your first love/ You can't wait to see her," it goes. "You borrowed the car and you think you're the driver/ But now you're the passenger to your own heart/ And it takes you travelling, travelling on." It is a song that is somehow both lament and celebration, and that saves its favourite wisdom for the chorus: "So fuel up your mind," it advises, "and fire up your heart and drive on."

As well-mannered and well-educated as they might seem, there is also ­something pleasingly insurrectionary to Stornoway. The Battery Human, for example, falls like a modern take on John Hartford's In Tall Buildings, rallying against a generation kept indoors and online: "Where are we going this fine morning?/ What are we doing this fine day?" it asks. "We're doing the same as every morning," comes the response. "We're staying inside on this fine morning/ We're staying inside on this fine day/ We'll stare at a screen like every morning." Their words carry just a pinch of the rebellion you feel as your new shoes rub at your heels and your shirt collar prickles your neck. They perhaps summed it up best in Zorbing, telling of the heart staging a lovestruck resistance to routine: "Send my body out to work," they sing, "but leave my senses in orbit over south-east London." It makes the perfect anthem for the new term.